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The development of low-cost and efficient electrocatalysts with a bicomponent active surface for reversible oxygen electrode reactions is highly desirable and challenging. Herein, we develop an effective calcination-hydrothermal approach to fabricate graphene aerogel-anchored Ni₃Fe-Co₉S₈ bifunctional electrocatalyst (Ni₃Fe-Co₉S₈/rGO). The mutually beneficial Ni₃Fe-Co₉S₈ bifunctional active components efficiently balance the performance of oxygen reduction and oxygen evolution reactions (ORR/OER), in which Co9S8 promotes the ORR and Ni₃Fe facilitates the OER. This balance behavior has an obvious advantage over that of monocomponent Ni₃Fe/rGO and Co₉S₈/rGO catalysts. Meanwhile, the additional synergy between porous rGO aerogels and Ni₃Fe-Co₉S₈ endows the composite with more exposed active sites, faster electrons/ions transport rate, and better structural stability. Benefiting from the reasonable material selection and structural design, the Ni₃Fe-Co₉S₈/rGO exhibits not only outstanding ORR activity with the high onset- and half-wave potentials (E onset = 0.91 V and E 1/2 = 0.80 V) but also satisfactory OER activity with a low overpotential at 10 mA cm⁻² (0.39 V). Moreover, rechargeable Zn-air cells equipped with Ni₃Fe-Co₉S₈/rGO exhibit excellent rechargeability and a fast dynamic response. Ministry of Education (MOE) This work was financially supported by the AcRF Tier 1 grant (RG17/16), Ministry of Education, Singapore; and National Natural Science Foundation of China (21875112).

The development of effective and affordable electrocatalysts for the oxygen reduction reaction (ORR) is critical for the renewable-energy technologies. Here, we present a new manganese iron oxide (MnFeO2) as a cost-effective material for the ORR with Pt-like electrochemical properties. Pyrolysis of hybrid agar hydrogel on NaCl nanocrystals furnishes a unique structure in which the active MnFeO2 particles are uniformly immobilized in the nitrogen-doped porous carbon aerogels (MnFeO2/NPC). Nitrogen-doped carbon is introduced to construct porous mass-transfer channels and reduce self-aggregation of the MnFeO2 particles. It is found that the formation of the MnFeO2 phase greatly depends on the pyrolysis temperature. Benefiting from the synergy of MnFeO2 and NPC, the MnFeO2/NPC can actually be as good as the Pt/C catalyst for the ORR, with an onset-potential of 0.98 V and a half-wave potential of 0.86 V, combined with demonstrating a superior stability and tolerance to methanol. This work was financially supported by the National Natural Science Foundation of China (NSFC Nos. 21875112 and 21576139), the National and Local Joint Engineering Research Center of Biomedical Functional Materials, and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

The development of high-efficiency electrocatalysts with low costs for the oxygen evolution reaction (OER) is essential, but remains challenging. Herein, a new synthetic process is proposed to prepare Ni3S4 particles embedded in N,P-codoped honeycomb porous carbon aerogels (Ni3S4/N,P-HPC) through a hydrogel approach. The preparation of Ni3S4/N,P-HPC begins with the sol–gel polymerization of tripolyphosphate, chitosan, and guanidine polymer that contains metal-binding sites, allowing for the uniform incorporation of Ni ions into the gel matrix, freeze-drying, and subsequent carbonization under an inert atmosphere. This synthesis resolves difficulties in synthesizing the pure Ni3S4 phase caused by the instability of Ni3S4 at high temperature, while affording good control of the porous structure and N,P-doping of carbon aerogels. The synergy between the structural advantages of N,P-carbon aerogels (such as easily accessible active sites, high specific surface area, and excellent electron transport) and the intrinsic electrochemical properties of Ni3S4 result in the outstanding OER performance of Ni3S4/N,P-HPC, with overpotentials as low as 0.37 V at 10 mA cm−2. The work outlined herein offers a simple and effective method for the development of carbon-based electrocatalysts for renewable energy conversion. This work was financially supported by the National Natural Science Foundation of China (NSFC; nos. 21875112 and 21576139), the Natural Science Foundation of Jiangsu Province (BK20180154), the National and Local Joint Engineering Research Center of Biomedical Functional Materials, and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

CuPt3 nanowires are synthesized with a thermosensitive amine-terminated poly(N-isopropylacrylamide) polymer, displaying “smart” temperature-controllable electrocatalytic activity towards the methanol oxidation reaction., Superior catalytic activity and stability for the methanol oxidation reaction of a direct methanol–air fuel cell is achieved with “clean” ultrathin CuPt3 wavy nanowires. The nanowires are synthesized for the first time by functionalizing CuPt3 nanoparticles with amine-terminated poly(N-isopropylacrylamide), a thermosensitive “smart” polymer having a phase transition at a liquid-electrolyte Tt (low critical solution temperature, 35 °C). Interestingly, retention of the functionalizing smart polymer on the surface of the nanowires reversibly switches the catalytic activity to lower rates above the Tt. The catalytic performance of the “clean” CuPt3 nanowires is shown to be significantly improved over that of commercial Pt black catalyst, owing to their unique structural advantages and bimetallic synergetic effect.